Electronic structure of Pu compounds with group-IIIB metals: Two regimes of behavior

Total energies of the fee structures [Pu,X=In, Ga, Al, or Tl] and L1(2)[Pu(3)X] structures are calculated with the full-potential LMTO method. Both the generalized gradient approximation and the local-density approxim ation are used. As expected each compound displays covalent bonding between the Pu df state and the X p state. Two regimes of behavior are seen: Pu3Al and Pu3Ga exhibit very similar properties (e.g., atomic volume, bulk modulus, formation energy, and density of states) as do Pu3In and Pu3Tl. The formation energies of Pu3In and Pu3Tl are 30 mRy/atom higher (less stable) than those of Pu3Al and Pu3Ga. The apparent instability in the latter compounds is linked to the degeneracies of the pdf hybridization near the Fermi energy and the consequent opportunity for Jahn-Teller/Peierls distortion.